1. Field of the Invention
The present invention relates generally to vibration sealing apparatus for sealing a rectangular end closure of a thermoplastic coated paperboard carton.
2. Description of the Prior Art
The prior art includes apparatus for sealing containers of thermoplastic material both by the direct application of heat, and by the generation of heat by vibration. The vibration is usually at a very high frequency, i.e. 20,000 cycles per second, and is frequently referred to as ultrasonic vibration. Examples of prior art apparatus of this type are disclosed in U.S. Pat. Nos. 3,200,557; 3,307,325; 3,309,841; 3,468,731; 3,531,908; 3,562,041; 3,579,958; 3,681,167; 3,717,539; and 3,912,576, as well as German Auslegeschrift 2,165,620.